The Torah in Parashat Emor (11:32) commands that if a Kohen had become impure and immersed in a Mikveh, he retains his status of impurity until dark – “U’ba Ha’shmesh Ve’taher” (“The sun shall set, and he shall then be pure”). This verse establishes a prohibition forbidding a Kohen from performing the Aboda (service in the Bet Ha’mikdash) after having becoming impure until “Ha’areb Shemesh” – nightfall. During the interim period between his immersion and nightfall, he is called a “Tebul Yom,” and he is forbidden from performing the Aboda during this time. The Sefer Ha’hinuch explains that as a Kohen serves as Beneh Yisrael’s “agent,” as it were, representing us before G-d, he must maintain the highest standards of cleanliness and purity as he ministers in the Mikdash. Therefore, when a Kohen becomes Tameh (impure), he may not perform the Aboda even after immersion, because a trace of Tum’a (impurity) remains even after immersion, and so he must wait until dark, when he is entirely divested of his spiritual impurity. This Halacha applies to all forms of impurity. It makes no difference whether the Kohen had been exposed to the severe forms of Tum’a, such as Sara’at, or contact with a human corpse, or if he had been exposed to a minor form of Tum’a, such as contact with the carcass of a rodent. In either case, he remains forbidden from performing the Aboda until nightfall after immersing. A “Tebul Yam” has a status called “Sheni Le’tum’a” (“second degree impurity”). This means that if he touches ordinary food, the food’s status is not affected, but if he touches Teruma or sacrificial food, the food becomes defiled. (This is because ordinary food can become only a “Sheni Le’tum’a,” whereas Teruma can become a “Shelishi Le’tum’a” and sacrificial food can become a “Rebi’i Le’tum’a.”) Rav Samson Raphael Hirsch (Frankfurt, Germany, 1808-1888) offers a beautiful insight to explain the underpinnings of this concept. He writes that after becoming Tameh, a person must undergo a fundamental change, which means leaving both his realm of space, and his realm of time. He therefore requires immersion, whereby he in essence leaves the earth, the dry land which is our normal habitat, and enters the water. Then, he must wait until nightfall, to enter a new zone in time, as it were. These two steps symbolize the process of transformation which must be undergone to divest oneself of impurity and regain his state of purity. The Halacha of “Tebul Yom” is subtly, and surprisingly, referenced by the very first Mishna, which speaks of the earliest time for the nighttime Shema recitation. The Mishna establishes that the earliest time for reciting Shema is “the time when the Kohanim come to eat their Teruma.” This refers to Set Ha’kochavim (nightfall, the time when the stars become visible), the point when Kohanim who had immersed become eligible to eat Teruma. Already the Gemara addresses the question of why the Mishna formulated this Halacha in such an unusual manner. Rather than simply and directly stating that the earliest time for the evening Shema is nightfall, the Mishna found it necessary to link the evening Shema with the law of “Tebul Yom,” which requires Kohanim to wait after immersing until nightfall before eating their hallowed food. The Igleh Tal (Rav Avraham Borenstein of Sochatchov, Poland, 1838-1910) explains the basis for this connection. He writes that the experience of reciting Shema in the morning leaves an impact upon the person, which remains until evening time, at which point he must recite Shema again. The impact of this recitation then endures until the morning, when we read it again. (Indeed, Rav Haim Vital taught that this is why we do not recite Shema at Minha – because the impact of the morning Shema remains with us until the evening.) Likewise, the exposure to Tum’a leaves an impression upon a person, and this impression continues even after immersion. The concept of “Tebul Yom” reflects this idea of an enduring impact whic